astr exam 2
What is the lower limit for the mass of a black hole?
3 solar masses
The astrophysicist who first calculated the highest mass that a dying star can have and still be a white dwarf was
S. Chandrasekhar
Astronomers have discovered pulsars spinning 500 x per second or more. How do astronomers think pulsars got to be spinning so outrageously fast?
Such fast-spinning pulsars have companion stars near them, which dump material on the pulsar and that spins it faster and faster
Which of the following statements about the mass of the Sun during its lifetime is correct?
The Sun will lose a significant amount of mass during and after its red giant phase
Which clock ticks more slowly?
The one at the bottom of that same mountain.
Which of the following is NOT a proof of the theory of General Relativity?
Time is observed to run more slowly in clocks when they are flown to high altitudes above the Earth.
Suspected black holes are detected as _____ in a binary
X-ray objects
Einstein suggested that the regular change (advance) in the perihelion of the planet Mercury could be explained by:
a distortion in spacetime caused by the gravity of the Sun
In a supernova like SN1987A, once the crisis of iron fusion has begun, roughly how long does it take the star's core to collapse?
a few tenths of a second
A member of the college football team wants to weigh as much as possible. Assuming he could somehow survive on all of them, at the surface of which object would he weigh the most? tip: Your "weight" is dependent on gravity. The force due to gravity is dependent on the mass of the celestial body you're on. For example, we "weigh" less on the moon than we do here on Earth because the moon has less mass and less gravity. Our mass stays the same. So how do the masses (or gravity) of the celestial bodies below compare?
a neutron star
When the mass of a star's core is greater than 1.4 times the mass of the Sun, degenerate electrons can't keep it stable as a white dwarf. Instead, it becomes:
a neutron star
Deep inside a black hole (and hidden from our view) is the compressed center, where all the "stuff" of the star goes. Astronomer call this central point
a singularity
Elements heavier than iron can be created during:
a supernova explosion
A charming friend of yours who has been reading a little bit about astronomy accompanies you to the campus observatory and asks to see the kind of star that our Sun will ultimately become, long, long after it has turned into a white dwarf. Why is the astronomer on duty going to have a bit of a problem satisfying her request?
after a white dwarf cools off it becomes too cold and dark to emit visible light
Which of the following stages will our own Sun go through in the future:
all of these
Which of the following stages will the Sun definitely go through as it gets older?
all of these choices
What type of main sequence star is most likely to become a black hole?
an O-type star
Suppose each of the following objects could collapse into a black hole. Each black hole would have a sphere around it that is the limit for escape -- once you are inside this region, you cannot get away. For which object would this region be the largest in diameter?
an entire galaxy of stars (with about a billion stars in it)
Astronauts falling into a black hole would not notice anything special happening as they fell through the Schwarzschild radius. Watching from the outside, we would see the astronauts
appear to get closer and closer to the Schwarzschild radius, but never arrive there.
Which of the following statements about the life of a star with a mass like the Sun is correct?
as the star is dying, a considerable part of its mass will be lost into space
In the model that astronomers have developed for pulsars, why do they suggest that there must be two beams of energy coming from the pulsar?
because neutron star beams come out of the north and south poles of a magnetic field
Why can a star with a mass like our Sun not fuse (produce) further elements beyond carbon and oxygen?
because they just cannot get hot enough for the fusion of heavier nuclei
Because white dwarfs are small, as their name implies, they are hard to see. What is a way astronomers have to find white dwarfs that distinguishes them from main sequence stars?
because white dwarfs get really hot, we can search for their ultraviolet radiation
Really massive stars differ from stars with masses like the Sun in that they
can fuse elements beyond carbon and oxygen in their hot central regions
According to the general theory of relativity, the presence of mass
causes a curvature (or warping) of spacetime
After the core of a massive star becomes a neutron star, the rest of the star's material
explodes outward as a supernova
If the Sun were to be spontaneously replaced by a blackhole of the same mass, the Earth would get sucked in.
false
Perfect linear alignment of a background source, lens, and observer will yield an Einstein cross.
false
When one member of a binary star system is a black hole, and astronomers detect flickering x-rays coming from the system, where are these x-rays usually coming from?
from a disk of material around the black hole (material that has been pulled from the companion star and is falling toward the black hole)
Astronomers have noticed that the visible filaments in the Crab Nebula are moving toward us at great speed. How can they know about motions like this?
from the Doppler shift in the line radiation from the nebula
What is a key reason that gravitational waves are so much harder to detect than electro-magnetic (e-m) waves?
gravitational waves are much weaker than e-m waves, and therefore require very, very precise equipment to detect
Black holes form when ___________________overcomes the outward________________produced by nuclear reactions within a star.
gravity; pressure
A handsome, rich, but vain movie star notices that he is starting to age, and consults you as his astronomy expert, to see if you can find an astronomical way to slow down his aging. Which of the following strategies would IN THEORY allow him to age more slowly than the rest of humanity.
he should travel to a black hole, and spend some time in orbit just above the event horizon
If stars with masses like our Sun's cannot make elements heavier than oxygen, where are heavier elements like silicon produced in the universe?
heavier elements are made in the cores of significantly more massive stars than the Sun, which can get hotter in the middle
General Relativity predicts that black holes have
infinite density
A star with a mass like the Sun which will soon die is observed to be surrounded by a large amount of dust and gas -- all material it has expelled in the late stages of its life. If astronomers want to observe the radiation from such a giant star surrounded by its own debris, which of the following bands of the spectrum would be the best to use to observe it?
infrared
Which of the following statements about the Crab Nebula is FALSE?
inside, there are a number of newly formed massive stars (O and B type stars)
If you trace back the history of a carbon atom in your little finger through all of cosmic history, where did this atom most likely originate?
it was fused from 3 helium nuclei in the core of a red giant star long before the Sun existed
To predict whether a star will ultimately become a black hole, what is the key property of the star we should look at?
mass
Wearing a very accurate watch, you volunteer to go on a mission to a black hole in a spaceship that has powerful rockets. You are able to orbit the black hole and stay a little distance outside of the event horizon. Compared to watches on Earth, your watch near the black hole will run:
more slowly
In a collapsing star of high mass, when electrons and protons are squeezed together with enormous force, they turn into a neutron and a:
neutrino
After a supernova event, the remaining core of the star may become a..
neutron star
After it experiences a "helium flash" a star like the Sun will have a brief period of stability, fusing helium into carbon (and sometimes oxygen). During this brief stable stage, the star
none of these
Pulsars "wobble" in their orbit because
of distortions in spacetime
If most stars are low-mass stars, and low-mass stars typically eject a planetary nebula, why then do astronomers see relatively few planetary nebulae in the sky?
planetary nebulae expand rapidly and soon become too faint to be visible
What kind of telescope did Jocelyn Bell use to discover pulsars in 1968?
radio
Which of the following is the largest (in diameter)?
red giant
Which choice has the objects ranked by size (radius), largest to smallest? (here, consider the singularity to be the size of a blackhole. The Schwarzchild radius describes the gravitational effect)
red giant, sun, white dwarf, neutron star, black hole
Why is it easier for red giants to lose mass than main sequence stars?
red giants are so big, the gravity at their surface (that holds material to the star) is less
Astronomer have concluded that pulsars are
rotating neutron stars
In order for a massive star to form a black hole, it must first ________________.
run out of fuel
Far away from a black hole (at the distance of another star), which of the following is a possible way to detect it?
search for flickering x-rays being given off from an accretion disk around the black hole, as it "eats" part of a neighbor star
A white dwarf, compared to a main sequence star with the same mass, would always be:
smaller in diameter
Astronomers observe a young cluster of stars, where stars with three times the mass of the Sun are still on the main sequence of the H-R diagram. Yet the cluster contains two white dwarfs, each with a mass less than 1.4 times the mass of the Sun. If we can show that the white dwarfs are definitely part of the cluster, how can their presence so soon in the life of the cluster be explained?
some stars can lose a lot of mass on their way to becoming white dwarfs; thus the white dwarfs could have started out as quite massive stars
When two identical atomic clocks, one on the ground floor and one on the top floor, are compared,
the clock on the ground floor ran a tiny bit slower
Astronomers believe that the many supernova explosions that happened in the Milky Way Galaxy could have played a role in the evolution of life over billions of years. How would they have influenced the development of life on Earth?
the cosmic rays produced by supernova explosions would have contributed to the rate of mutations over many generations
If observations of supernovae in other galaxies show that such an explosion happens in a spiral galaxy like the Milky Way on average every 25 to 100 years, why have astronomers on Earth not seen a supernova explosion in our Galaxy since 1604?
the disk of our Galaxy contains a great deal of dust, which tends to block the light of supernova explosions from more distant parts of our Galaxy
Which of the following is a characteristic of degenerate matter in a white dwarf star?
the electrons get as close to each other as possible and resist further compression
The region around a black hole where everything is trapped, and nothing can get out to interact with the rest of the universe, is called
the event horizon
If we look back to the first generation of stars made when the Galaxy was first forming, how do they differ from stars being formed today?
the first generation stars contain little or no elements heavier than helium
Once a black hole forms, the size of its event horizon is determined only by
the mass inside the event horizon
In the far future, a starship becomes trapped inside the event horizon of a black hole. Although the crew discovers that their ship cannot out, they at least want to send a message to other ships in the area to stay away from the danger zone. If they send out a message in the form of a radio wave, what will be its fate?
the message will never emerge from the event horizon
Which of the following is NOT a result of supernova explosions?
the neutron star is disrupted and tears apart into many pieces
Which of the following is one reason we do not detect a pulsar in many remnants of supernova explosions? (Careful! This one is tricky!)
the pulsar beam doesn't happen to point toward us in many cases
Many names used by astronomers are misleading or outdated. A good example is the term planetary nebula,which astronomers use to refer to:
the shell let go by a dying low-mass star
According to Einstein's general theory of relativity, the stronger a star's gravity,
the slower time runs near it
Which of the following statements about the way the mass of a white dwarf affects spacetime is correct?
the white dwarf mass will curve spacetime; light has to follow that curvature
When stars become giants, which of the following does NOT usually happen?
their mass grows significantly as they incorporate planets and interstellar matter near the star
Your sweetheart gives you a piece of gold jewelry as a present to celebrate your passing your astronomy class. Where did the gold atoms in that gift originally come from (where were they most likely made)?
they were built up from smaller nuclei during a supernova explosion
In a planetary nebula, the shell of expelled material is glowing intensely. What is the main source of energy for this glow?
ultraviolet radiation from the collapsing hot star at the center
When neutron stars were first predicted theoretically, no scientist expected to be able to detect one of them across interstellar distances. What enabled astronomers to find neutron stars in the late 1960's?
we found strongly magnetic neutron stars whose whirling beams of energy were detected as pulsars
When a single star with a mass equal to the Sun dies, it will become a
white dwarf
Which of the following stages can only occur in the life of a low-mass star (whose final mass is less than 1.4 times the mass of the Sun)?
white dwarf
Which are listed in the order of their increasing density?
white dwarfs, neutron stars, black holes
If gas approaches a black hole, it will often heat up and emit ________________ that can be detected telescopically.
x-ray
